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Iberia is predicted under future warming scenarios to be increasingly impacted by drought. While it is known that this region has experienced multiple intervals of enhanced aridity over the Holocene, additional hydroclimate-sensitive records from Iberia are necessary to place current and future drying into a broader perspective. Toward that end, we present a multi-proxy composite record from six well-dated and overlapping speleothems from Buraca Gloriosa (BG) cave, located in western Portugal. The coherence between the six stalagmites in this composite stalagmite record illustrates that climate (not in-cave processes) impacts speleothem isotopic values. This record provides the first high-resolution, precisely dated, terrestrial record of Holocene hydroclimate from west-central Iberia. The BG record reveals that aridity in western Portugal increased secularly from 9.0 ka BP to present, as evidenced by rising values of both carbon (δ13C) and oxygen (δ18O) stable isotope values. This trend tracks the decrease in Northern Hemisphere summer insolation and parallels Iberian margin sea surface temperatures (SST). The increased aridity over the Holocene is consistent with changes in Hadley Circulation and a southward migration of the Intertropical Convergence Zone (ITCZ). Centennial-scale shifts in hydroclimate are coincident with changes in total solar irradiance (TSI) after 4 ka BP. Several major drying events are evident, the most prominent of which was centered around 4.2 ka BP, a feature also noted in other Iberian climate records and coinciding with well-documented regional cultural shifts. Substantially, wetter conditions occurred from 0.8 ka BP to 0.15 ka BP, including much of the ‘Little Ice Age’. This was followed by increasing aridity toward present day. This composite stalagmite proxy record complements oceanic records from coastal Iberia, lacustrine records from inland Iberia, and speleothem records from both northern and southern Spain and depicts the spatial and temporal variability in hydroclimate in Iberia.
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Expression of the “4.2 ka event” in the southern Rocky Mountains, USA
Abstract. The use of the climatic anomaly known as the “4.2 ka event” as thestratigraphic division between the middle and late Holocene has prompteddebate over its impact, geographic pattern, and significance. The anomalyhas primarily been described as abrupt drying in the Northern Hemisphere atca. 4 ka (ka, thousands of years before present), but evidence of thehydroclimate change is inconsistent among sites both globally and withinNorth America. Climate records from the southern Rocky Mountains demonstratethe challenge with diagnosing the extent and severity of the anomaly.Dune-field chronologies and a pollen record in southeastern Wyoming revealseveral centuries of low moisture at around 4.2 ka, and prominent low standsin lakes in Colorado suggest the drought was unique amid Holocenevariability, but detailed carbonate oxygen isotope (δ18Ocarb) records from Colorado do not record drought at the sametime. We find new evidence from δ18Ocarb in a smallmountain lake in southeastern Wyoming of an abrupt reduction in effectivemoisture or snowpack from approximately 4.2–4 ka, which coincides in timewith the other evidence of regional drying from the southern Rocky Mountainsand the western Great Plains. We find that the δ18Ocarb inour record may reflect cool-season inputs into the lake, which do not appearto track the strong enrichment of heavy oxygen by evaporation during summermonths today. The modern relationship differs from some widely appliedconceptual models of lake–isotope systems and may indicate reduced winterprecipitation rather than enhanced evaporation at ca. 4.2 ka.Inconsistencies among the North American records, particularly in δ18Ocarb trends, thus show that site-specific factors can preventidentification of the patterns of multi-century drought. However, theprominence of the drought at ca. 4 ka among a growing number of sites in theNorth American interior suggests it was a regionally substantial climateevent amid other Holocene variability.
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- Award ID(s):
- 1903729
- PAR ID:
- 10413867
- Date Published:
- Journal Name:
- Climate of the Past
- Volume:
- 18
- Issue:
- 5
- ISSN:
- 1814-9332
- Page Range / eLocation ID:
- 1109 to 1124
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Global climate during the Holocene was relatively stable compared to the late Pleistocene. However, evidence from lacustrine records in South America suggests that tropical latitudes experienced significant water balance variability during the Holocene, rather than quiescence. For example, a tight coupling between insolation and carbonate δ18O records from central Andean lakes (e.g., Lakes Junín, Pumacocha) suggest water balance is tied directly to South American summer monsoon (SASM) strength. However, lake carbonate δ18O records also incorporate information about temperature and evaporation. To overcome this ambiguity, clumped and triple oxygen isotope records can provide independent constraints on temperature and evaporation. Here, we use clumped and triple oxygen isotopes to develop Holocene temperature and evaporation records from three central Andean lakes, Lakes Junín, Pumacocha, and Mehcocha, to build a more complete picture of regional water balance (P–E). We find that Holocene water temperatures at all three lakes were stable and slightly warmer than during the latest Pleistocene. These results are consistent with global data assimilations and records from the foothills and Amazon basin. In contrast, evaporation was highly variable and tracks SASM intensity. The hydrologic response of each lake to SASM depends greatly on the physical characteristics of the lake basin, but they all record peak evaporation in the early to mid‐Holocene (11,700 to 4,200 years BP) when regional insolation was relatively low and the SASM was weak. These results corroborate other central Andean records and suggest synchronous, widespread water stress tracks insolation‐paced variability in SASM strength.more » « less
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none (Ed.)Abstract The South American monsoon is central to the continent’s water and energy cycles, however, the relationships between the monsoon, regional water balance, and global climate change is poorly understood. Sediment records at Lake Junín (11°S, 76°W) provide an opportunity to explore these connections over the last 650 ka. Here, we focus on two interglacials, the Holocene (11.7–0 ka) and MIS 15 (621–563 ka), when sediment proxies suggest rapid regional hydroclimate fluctuations occurred. Clumped isotope distributions of lake carbonates reveal that interglacial water temperatures were similar to present, though analytical limitations preclude detecting the small temperature differences expected in the tropics (<2 °C). Combining the reconstructed water temperatures with carbonate oxygen (δ18O) and triple oxygen (Δ′17O) isotope values, we reconstruct precipitation δ18O values and lake water Δ′17O values. Precipitation δ18O values, a proxy of monsoon strength, range from -18.6 to -12.3 ‰ with lower values reflecting a stronger monsoon. Lake water Δ′17O values are -14 to 43 per meg and indicate the extent of lake water evaporation; lower values reflect a higher proportion of evaporation to inputs (i.e., more negative P-E). The precipitation δ18O and lake water Δ′17O values from both interglacials vary with the pacing of local summertime insolation, which follows an orbital pacing. These data document the close connection between Andean water balance, the South American monsoon, and global climate. Further, we analyze the relationship between precipitation δ18O and insolation, and we find that the relationship is consistent among interglacials, suggesting a similar response of the monsoon to orbital forcings over time. In contrast, while lake water Δ′17O and insolation are also correlated during both interglacials, water balance was overall more positive during MIS 15 than the Holocene. This suggests that either other global forcings or local basin dynamics can also contribute to water balance at Lake Junín. Together, these data provide new evidence of the connections between global climate, monsoon strength, and regional water balance.more » « less
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The 8.2 ka event is the most significant global climate anomaly of the Holocene epoch, but a lack of records from Mainland Southeast Asia (MSEA) currently limits our understanding of the spatial and temporal extent of the climate response. A newly developed speleothem record from Tham Doun Mai Cave, Northern Laos provides the first high resolution record of this event in MSEA. Our multiproxy record (d18O, d13C, Mg/Ca, Sr/Ca, and petrographic data), anchored in time by 9 U-Th ages, reveals a significant reduction in local rainfall amount and weakening of the monsoon at the event onset at ~8.29 +/- 0.03 ka BP. This response lasts for a minimum of ~170 years, similar to event length estimates from other speleothem d18O monsoon records. Interestingly, however, our d13C and Mg/Ca data, proxies for local hydrology, show that abrupt changes to local rainfall amounts began decades earlier (~70 years) than registered in the d18O. Moreover, the d13C and Mg/Ca also show that reductions in rainfall continued for at least ~200 years longer than the weakening of the monsoon inferred from the d18O. Our interpretations suggest that drier conditions brought on by the 8.2 ka event in MSEA were felt beyond the temporal boundaries defined by d18O-inferred monsoon intensity, and an initial wet period (or precursor event) may have preceded the local drying. Most existing Asian Monsoon proxy records of the 8.2 ka event may lack the resolution and/or multiproxy information necessary to establish local and regional hydrological sensitivity to abrupt climate change.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/cp-18-1109-2022
